The present invention relates to an electromagnetic wave attenuating transparent member, and it is preferably related to an electromagnetic wave attenuating transparent member having an antireflection effect, in particular.
In recent years, there have been doubts that electromagnetic waves emitted from office automation equipment, cathode-ray tubes of television sets and other electronic equipment might have an influence on the human body, and a growing interest in this matter is now taken.
A method which was taken frequently in the past to avoid the influence of these electromagnetic waves was to cover with a conductive member capable of looking through like a wire net.
However, when a cathode-ray tube is covered with the conductive member, a screen becomes hard to be observed, resulting in fatigue of eyes of a user, which has been a problem.
In view of the foregoing, there has been proposed a technology wherein a layered body representing a light-transmitting thin film is provided on the surface of a screen in place of a net of metal fine wires, in order to obtain not only an effect of attenuating electromagnetic waves but also an effect of preventing reflection. For example, in the technology disclosed in TOKKAIHEI No. 6-34801, there is used a three-phase layered body which has a layer of indium tin oxide (ITO) as a transparent and conductive layer, a layer of silicon oxide as a low refractive index layer, and a layer of titanium oxide as a high refractive index layer in this order from the base material. In this technology, however, the transparent and conductive layer is as thin as 300 .ANG. in thickness and an effect of shielding electromagnetic waves is small, resulting in insufficient effects, although the screen became easy to see due to the effect of preventing reflection.
In the technology disclosed in TOKKAIHEI No. 11-73119, on the other hand, a high refractive index layer contains indium tin oxide as a material and its thickness is made to be 1000 .ANG. or more to serve as a transparent and conductive layer in the layer structure of a light-transmitting low refractive index layer and a light-transmitting high refractive index layer.
Owing to a conductive layer which has been made thick, sheet resistivity has been lowered, and an effect of shielding electromagnetic waves has been improved, resulting in efficiency which is sufficient in practical use. However, when stored under the environmental conditions of high temperature and high humidify, a coated layer tended to have color unevenness and to be floated off, which have been problems of resistance to surroundings. In particular, when the coat mentioned above was formed on the transparent plastic base material, these problems were noticeable.
With regard to the coat representing a thin film having the effect of shielding electromagnetic waves stated above, an occasion where it is provided on a transparent member having a curved surface like a lens is also considered in addition to an occasion where it is provided on a flat transparent base material or on a transparent base film material. When coating a thin layer having the effect of shielding electromagnetic waves mentioned above on a positive meniscus type lens, it was normal to coat on the concave surface. This was to prevent occurrence of scratches and to prevent dirt. However, in the case of a coat for electromagnetic wave attenuation and for prevention of reflection which has a transparent and conductive layer with a thickness of 1000 .ANG. or more and is coated on a concave surface, there has been a problem that exfoliation of the coat and color unevenness of the coat color were caused by expansion and contraction of the lens base material when the coat was left for one week under the conditions of high temperature of 60.degree. C. and high humidity of 90%.
When coating a thin layer having an effect of shielding electromagnetic waves on a positive meniscus lens and coating it on a negative meniscus lens, the direction of deformation of the lens is changed. It was therefore found that it is necessary to determine whether to coat on the convex surface of the lens or to coat on the concave surface of the lens, taking the direction of deformations in each lens into consideration.